This invention relates to a high efficiency furnace containing a secondary condensing heat exchanger and, in particular, to an improved secondary heat exchanger construction.
Many condensing furnaces containing secondary heat exchangers utilize flared entrance and exit ports for connecting each of the heat exchanger cells to opposed cell panels. The entrance and exit ports are typically round or oval cylinders that extend outwardly from the end walls of the cell housing. The cylinders are passed through openings formed in the cell panels and the ends of the cylinders are expanded or coined radially adjacent to the front face of the panel. To close the joint between the end of the cylinder and the panel, the joint region is filled with RTV. Typically, an excess of RTV is employed in an effort to fully close the joint. This procedure is wasteful and too much RTV can overfill the joint and create performance problems. By the same token, under filling of the joint can create leaks in the joint region, again leading to poor furnace performance.